1. Technical Field
The present disclosure relates to cooling fans, and particularly to a cooling fan which has a reduced noise when an impeller thereof rotates.
2. Description of Related Art
It is well known that if heat generated by electronic components, such as integrated circuit chips, is not efficiently dissipated during operation, these electronic components may suffer damage. Thus, cooling fans are often used to cool the electronic components.
A typical cooling fan includes a housing, a cover on the housing, and a stator and an impeller received in a space defined between the housing and the cover. The housing includes a bottom wall and a sidewall extending upwardly from the bottom wall. The sidewall defines an air outlet therein. The air outlet includes a near side and a rear side at two opposite sides. A tongue is formed adjacent to the rear side of the air outlet. The tongue extends from the sidewall into the space between the housing and the cover, and protrudes toward the impeller. The impeller includes a hub and a plurality of blades extending radially and outwardly from the hub. An air channel is defined between free ends of the blades and the sidewall of the housing with a width increasing from the rear side toward the near side of the air outlet, so as to increase a pressure of an airflow generated by the impeller.
When the cooling fan operates, the blades of the impeller drive air therebetween to rotate to generate forced airflow, and then the airflow flows along the air channel to the air outlet. However, when the airflow flows through the tongue, the airflow separates from the tongue and generates a vortex thereat. The vortex strikes the tongue and thus generates noise which makes a user near the cooling fan feel uncomfortable.
What is needed, therefore, is a cooling fan which overcomes the above-described limitations.